In order to explore the possibility of modifying the surface of silk fabrics with graft process by use of UV light irradiation, Electron-spin resonance (ESR) studies were carried out to detect the radicals induced on the surface of silk fabrics exposed to three kinds of UV light sources at room temperature. And similar ESR signals were observed. The results indicate that UV-rays can produce free radicals on the surface of silk fibers without external additives or co-additives and oxygen might affect the radical spectra and concentration. From the analysis of ESR spectra, it is found that UV-light may be a tool to improve the surface properties of silk fabrics by grafting monomers onto the silk polymer chains.